1. Field of the Invention
The present invention relates to medical devices, for example, radiotherapy apparatuses and CT (computed tomography) apparatuses.
2. Description of Related Art
Stereotactic radiotherapy apparatuses are known medical devices for performing treatment by irradiating an affected area, such as a tumor, with radiation. Such Stereotactic radiotherapy apparatuses emit radiation a plurality of times in multiple directions towards the same affected area. To emit radiation from multiple directions, it is necessary to dispose a radiation emitter at a position corresponding to a location for emitting the radiation for irradiating the affected area, and to allow the radiation detector to be moved to a plurality of positions around the patient and aligned. Known approaches for moving the radiation emitter in this way include the cantilever type, robotic arm type, and gantry type approaches.
In the cantilever type approach, the radiation emitter is supported in a cantilevered manner and rotated around the patient's body. In the robotic arm type approach, the radiation emitter is attached to the end of a multi-axis arm, and the radiation is emitted from an arbitrary direction. However, with the cantilever type approach or the robotic arm type approach, because of a structure for attaching the radiation emitter to the end of the cantilever or the arm, the cantilever or the arm becomes deformed due to the weight of the radiation emitter, thus making high-precision positioning (setting the irradiation direction) difficult.
In contrast, in the gantry type approach, a gantry is positioned so as to surround a patient lying on a couch, and the radiation emitter is moved along the gantry or together with the gantry. The gantry type approach is a preferable structure for realizing high-precision positioning because the radiation emitter is supported by a highly rigid gate-shaped gantry. Medical devices using this gantry type approach have been disclosed, for example, in Japanese Translation of PCT International Application, Publication No. HEI-10-511595, which is related to a radiotherapy apparatus described below, and Japanese Unexamined Patent Application, Publication No. HEI-10-71213, which is related to a proton-beam therapy apparatus.
With the cantilever type approach and the gantry type approach, to increase the degrees of freedom of the irradiation direction, positioning control (translation and rotation) of the couch on which the patient is set is performed, in addition to movement of the radiation emitter in a single direction.